Composite articles comprising or consisting of a polymer (usually a continuous phase, and possibly comprising fluoropolymer(s) and fibers (such as glass fibers, carbon fibers, and graphite fibers) are well known in the art. The addition of fiber to a matrix polymer can improve certain properties of the polymer. These properties can include creep resistance, tensile strength and modulus, and flexural strength and modulus. The reinforcing fiber chosen generally has a higher tensile modulus and strength than the polymer alone. When a fluoropolymer is used as the matrix polymer, as described herein, the resulting composite often has many of the attributes of fluoropolymers such as high temperature resistance and chemical resistance, which make such composites useful as parts, for example, for the chemical processing industry. It is among the objects of this invention to provide a method for the production of such polymer composites that exhibit improved properties and to provide articles made by the method.
Background information regarding producing composites of polymer and fiber or fibers can be found in Polymeric Materials Encyclopedia, by Joseph C. Salamone (Jul. 23, 1996), ISBN-10: 084932470X, ISBN-13: 978-0849324703 pages 8327-8343.
Some background in double-belt press lamination is found in “Modelling of heat transfer in thermoplastic composites manufacturing: double-belt press lamination” by A. Trende, B. T. Astrom, A. Woginger, C. Mayer, M. Neitzel, in Composites Part A: Applied Science and Manufacturing, Volume 30, Issue 8, August 1999, Pages 935-943.
Known related methods and articles include but are not necessarily limited to U.S. Pat. No. 5,470,409 to Deakyne et al., issued Nov. 28, 1995, entitled “Process for making fluoropolymer composites,” U.S. Pat. No. 5,232,975 to Deakyne, issued Aug. 3, 1993, entitled “Preconsolidation process for making fluoropolymer composites,” U.S. Pat. No. 4,163,742 to Mansure, issued Aug. 7, 1979, entitled “Process and product prepared from tetrafluoroethylene polymer and graphite fibers,” U.S. Pat. No. 5,427,731 to Chesna et al., issued Jun. 27, 1995, entitled “Compression molding of structures,” and U.S. Pat. No. 7,011,111 to Spiegl et al., issued Mar. 14, 2006, entitled “Sealing elements for compressor valves”.
Additional known related methods and articles include but are not necessarily limited to U.S. Pat. No. 5,759,927 to Meeker, issued Jun. 2, 1998, entitled “Glass-fiber-containing non-woven polymer web, and process for preparing same,” and U.S. Pat. No. 5,460,764 to Held, issued Oct. 24, 1995, entitled “Method and apparatus for making highly densified sheets”.
There remains a need for any one or combinations of improvements in these fields, including but not limited to: a simplified process of manufacture; a robust and/or reproducible process of manufacture that can produce robust and/or reproducible product; a process to produce an article of increased density; an article of increased density; a process to produce products having fewer metal, metallic, ionic, or related impurities, particularly for processes that include a solvent or water; a process for using fibers that preserves fiber length; a process to produce product having a uniform property throughout a useful volume; any process to produce a composite product having a directional property (such as tensile strength, compressive strength, or elongation to break) that is uniform or superior regardless of the direction of measurement (or uniform or superior in one direction, or uniform or superior in two orthogonal directions), and the like.
These improvements are sought in areas where composite articles are used, e.g. equipment for semiconductor manufacture, in aircraft parts, in automotive parts, in gaskets, in seals, and the like.